That's an area that I'm also very interested in!
I'd love to see this happen, but realistically, the VFX industry is just too deep in C++ so I don't expect anything to happen any time soon. For exploration purposes though I guess you could just write everything that you need in Rust (as a lib crate) and then compile it to a shared library that uses the C ABI (e.g.:
https://valerioviperino.me/rust-cpp-ffi), then use the bare minimum of the HDK to use your library using the usual "blessed" C++ workflow (e.g.:
https://www.sidefx.com/docs/hdk/_h_d_k__intro__creating_plugins.html).
Worth giving it a try for sure.. now you made me curious to see if it's feasible